What do you understand by isoelectronic species? Name a species that will be isoelectronic with each of the following atoms or ions.
$(i)$ $F^{-}$ $(ii)$ $Ar$ $(iii)$ $Mg^{2+}$ $(iv)$ $Rb^{+}$

(N/A) Isoelectronic species are atoms or ions that contain the same number of electrons.
$(i)$ $F^{-}$ has $9+1 = 10$ electrons. An isoelectronic species is $Ne$ ($10$ electrons).
$(ii)$ $Ar$ has $18$ electrons. An isoelectronic species is $Cl^{-}$ ($17+1 = 18$ electrons).
$(iii)$ $Mg^{2+}$ has $12-2 = 10$ electrons. An isoelectronic species is $Na^{+}$ ($11-1 = 10$ electrons).
$(iv)$ $Rb^{+}$ has $37-1 = 36$ electrons. An isoelectronic species is $Kr$ ($36$ electrons).